1. Field of the Invention
The present invention relates to a positioning apparatus for a stage or the like used in an apparatus or method for manufacturing devices such as semiconductor devices and liquid crystal displays. The positioning apparatus is used in, for example, a projection exposure apparatus, various precise processing apparatuses and measuring apparatuses, etc., for moving and positioning a substrate such as a semiconductor wafer, a mask, and a reticle at high speed and with high accuracy. In addition, the present invention may also be applied to a method for manufacturing a semiconductor device by using an exposure apparatus incorporating such a positioning device.
2. Description of the Related Art
FIG. 12 shows a perspective view of an XY stage as an example of a known positioning device. A positioning device of this type is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 8-229759.
In FIG. 12, reference numeral 42 denotes a base which supports a stage device and includes a reference surface 43, and reference numeral 38 denotes a fixed Y guide which is fixed to the base 42 and whose side surface serves as a reference surface. In addition, reference numeral 37 denotes a Y stage which serves as a moving body. The Y stage 37 is guided by the fixed Y guide 38 and is moved in a Y direction by Y linear motors 41 disposed at both ends thereof, each Y linear motor 41 including a fixed member 39 and a movable member 40. Reference numeral 32 denotes an X stage which includes movable members (not shown) of X linear motors. The X stage 32 is guided by an X guide 33 provided on the Y stage 37 and receives a thrust from fixed members 34 of the X linear motors which are also provided on the Y stage 37.
As shown in FIG. 12, a top plate 31 of the X stage 32 has a flat shape, and an X-direction mirror 45 and a Y-direction mirror 46 used for position measurement in the X and Y directions, respectively, are disposed on the top plate 31. The position measurement is performed by irradiating the mirrors with a laser beam and detecting the reflected light.
When a θZT driving mechanism shown in FIG. 16 is installed in this stage device, movements in a Z direction, which is a direction parallel to, for example, an optical axis of an exposure system, and in rotational directions around the X, Y, and Z axes (θx, θy, θz) are also possible.
The upper portion of the X stage 32 shown in FIG. 12 corresponds to a base plate 151 shown in FIG. 16. A cylindrical fixed member 202 is provided on the base plate 151, and a porous pad 207 attached to the fixed member 202 retains an internal surface of a guiding member 203 without contacting it. The guiding member 203 is formed integrally with a top plate 204, which corresponds to the top plate 31 used for supporting a wafer and a wafer chuck (not shown). The base plate 151 can be rotated around the central axis thereof by a θ linear motor 216, and can be reciprocated in the vertical direction in FIG. 16 by Z linear motors 215 which are arranged along the circumferential direction at constant intervals.
FIG. 13 is a block diagram for each degree of freedom in the known positioning apparatus. Reference numeral 57 denotes mechanical characteristics Go of the positioning apparatus. According to the mechanical characteristics Go, a displacement x is output when a force f is input. Reference numeral 58 denotes controller characteristics Gc including characteristics of a proportional-integral-differential (PID) controller, amplifier characteristics, and stabilization filters. According to the controller characteristics Gc, a predetermined force f is output when the difference obtained by subtracting the displacement x from a desired position xr is input. For example, in position control in the X and Y directions, the output of a laser interferometer is used to determine the displacement x. The performance of the positioning apparatus is determined by how quickly and accurately the desired position can be tracked in each degree of freedom.
FIG. 14 is a diagram showing gain/phase characteristics of the control system of the known positioning apparatus. The gain/phase characteristics shown in FIG. 14 are the combination of the mechanical characteristics Go and the controller characteristics Gc shown in FIG. 13, and are called loop transfer characteristics. In order to obtain high-speed, high-accuracy tracking performance, the gain characteristics of the positioning apparatus are preferably made as high as possible. However, the mechanical characteristics Go include various natural frequencies, and the plate-shaped stage component 31 used in the known positioning apparatus may have a natural frequency with a high peak (weak damping) in a low-frequency region (from 300 Hz).
When vibration of the stage components occurs, the mirrors mounted on the stage for position measurement also vibrate and the positioning accuracy is reduced.
In addition, since oscillation occurs at the natural frequency when the gain is too high, the gain characteristics of the control system are limited. In FIG. 14, the zero-crossing frequency, which serves as an index of the gain level, is approximately 40 Hz.
Accordingly, it is necessary to suppress the peak by using stabilization filters such as low-pass filters and notch filters. Alternatively, the system is designed such that the natural frequency is increased to a high-frequency region.
In Japanese Unexamined Patent Application Publication No. 11-142555, for example, a stage component having a hollow structure is disclosed. With reference to FIG. 15, reference numeral 411 denotes a top plate unit included in an X stage. The top plate unit 411 is formed of ceramic and has a hollow structure as shown in the figure. This hollow structure 421 is constructed of two or more ceramic members and has an injection hole 431 at the bottom thereof. After the two or more members are baked, they are bonded together by a resintering process. In the resintering process, the members are generally bonded together by glass bonding using an alumina-based material having a coefficient of thermal expansion which is close to that of the members. However, when a material having a small coefficient of thermal expansion is used in order to suppress the thermal deformation of the top plate unit 411, there is the risk that sufficient bonding strength cannot be obtained. In addition, when an adhesive is used for bonding the members together, there is the risk that sufficient adhesive strength and adhesive reliability cannot be obtained.
In the above-described example, in order to move the top plate supporting the substrate, such as a wafer, to a predetermined position in the XY plane, the base plate is moved in the X and Y directions by the XY stage unit while the position of the top plate in the XY plane is determined by laser interferometers. In addition, the top plate receives a driving force from the base plate through radial air bearings. The top plate thus moves to the predetermined position. At this time, the top plate and the base plate preferably move together. However, in actuality, the driving force is applied to the top plate with a phase lag with respect to the movement of the base plate in correspondence with the compression of the air in the radial air bearings.
In order to prevent this, the radial air bearings may be omitted and Lorentz force actuators (linear motors) used in the θZT driving mechanism may also be used for fine movement in the X and Y directions. However, in such a case, it is extremely difficult for the Lorentz force actuators (linear motors) to generate enough force to hold the weight of the top plate, the wafer and the wafer chuck mounted on the top plate as well as to accelerate them because of restrictions on the size of the motors and heat emitted from the motors.
In addition, in the positioning apparatus of the known art such as the XY stage unit disclosed in the Japanese Unexamined Patent Application Publication No. 8-229759, because the top plate 204 is formed as a solid plate, the natural frequency thereof cannot be increased. In addition, when the hollow structure 42 disclosed in the Japanese Unexamined Patent Application Publication No. 11-142555 is used, the hollow structure cannot be formed if there is a difference in the coefficient of thermal expansion between the ceramic bonding material and the material of the hollow structure. Accordingly, materials having small coefficients of thermal expansion cannot be used. In addition, when an adhesive is used, differences occur between components even when they are formed in the same shape, and the natural frequency of the combined unit cannot be as high as a calculated or theoretical value because of differences between adhesion conditions.
In addition, when a material having a small coefficient of thermal expansion is used, since the top plate is formed as a solid plate, the thickness of the top plate is increased in order to ensure sufficient rigidity. Thus, the weight of the top plate is considerably increased relative to the increase in rigidity. Accordingly, the load placed on the above-described linear motors for acceleration is increased, and a current necessary to hold this acceleration is also increased. In addition, heat emitted from the linear motors increases proportionally to the square of the current. This degrades the environment around the wafer, and a problem occurs in that the alignment accuracy and stage accuracy are adversely affected and productivity is reduced when high-speed micromachining of semiconductor devices is required.